The present invention relates generally to energy transfer devices such as engines and motors, and more particularly, to an engine having a cylinder, a driveshaft rotatably supported within the cylinder, and at least one piston slidably mounted within the cylinder wherein the driveshaft includes a generally helical track formed thereon and including a ratcheted clutch coupled to the piston and engaging the helical track for converting reciprocal motion of the piston to rotational motion of the driveshaft.